Study On Process And Properties Of Ultrasonic Electroless Plating On AZ91D Magnesium Alloy

Magnesium and its alloys are the lightest metal structure materials in industrial applications.China's magnesium is rich in resources and reserves are the first in the world.Magnesium alloy production and export volume are also among the best in military defense,aerospace and automobile fields.However,the oxide film formed on the surface of magnesium alloy is not dense,unstable in solution,poor corrosion resistance,limiting its application.Surface modification technology is an important means to improve the corrosion resistance of magnesium alloy.Electroless plating can get good corrosion resistance and wear resistance.In this paper,the ultrasonic field was introduced into the electroless plating process of AZ91 D magnesium alloy,and the pretreatment process parameters were optimized by single factor test.The parameters of ultrasonic plating were optimized by orthogonal test.The heat treatment parameters were optimized by single factor test.Finally,it was taken at intervals to extend the bath life method.The surface morphology,composition,film thickness,corrosion resistance,abrasion resistance,deposition rate and binding strength of the electroless plating were measured by scanning electron microscopy,X-ray diffractometer,electrochemical workstation and friction and wear tester.The results show that the ultrasonic field can significantly improve the deposition rate of electroless plating,improve the pretreatment surface quality,enhance the binding force,the uniform thickness of the prepared electroless coating is complete and the deposition rate is increased by 0.2083 ?m / min.Under the experimental conditions,the optimum pretreatment parameters are: pickling time 30 s,activation time 10 min;The best electroless plating process parameters are: temperature 85 ?,time 60 min,ultrasonic power 80 W,p H 6.0.The self-corrosion potential of the magnesium alloy after electromechanical plating is shifted by 0.902 V,which significantly improves the corrosion resistance of the magnesium alloy.After the electroless plating,the surface of the coating is uniform,compact and smooth,and its friction coefficient is determined by the substrate 0.23 reduced to 0.14,significantly enhance the wear resistance of magnesium alloy.After 300 ?× 1 h heat treatment,the sample binding force than the untreated sample was significantly improved nearly doubled,then the hardness of the coating reached a peak of 890 HV.Chemical bath for 4 consecutive cycles,the black precipitate generated,the bath becomes turbid,the interval of liquid can make the chemical bath to improve the service life of more than 2 times.